Have you ever deleted a 40GB folder, emptied the Trash, and discovered that your free storage didn't increase by a single gigabyte? This common issue is almost always caused by APFS local snapshots.
When Time Machine is enabled, macOS automatically creates hourly local snapshots on your internal APFS container. When you delete a file, APFS preserves the physical storage blocks if an active snapshot references them.
XrayMac identifies active APFS local snapshots and allows you to thin obsolete snapshots safely without impacting your external Time Machine backups.